Method and device for reflective display with time sequential color illumination

ABSTRACT

In various embodiments of the invention, a display device comprises an illumination apparatus configured to emit light of a different color at different times and at least one interferometric light modulating device illuminated by the illumination apparatus. In certain preferred embodiments, interferometric light modulating devices are illuminated for short durations with different color light, the durations of the time being sufficiently short to produce color fusion or blending of colors as perceived by the human eye. The interferometric light modulating device may comprise a white interferometric light modulating device that reflects white light in one state. The interferometric light modulating device may also have a reflectivity spectrum that includes a least two color peaks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 60/613,375, filed on Sep. 27, 2004, which ishereby incorporated by reference in its entirety.

BACKGROUND

The field of the invention relates to micro-electro-mechanical (MEMS)systems. More specifically, the invention relates to light modulation,including interferometric light modulation.

MEMS include micro mechanical elements, actuators, and electronics.Micromechanical elements may be created using deposition, etching, andor other micromachining processes that etch away parts of substratesand/or deposited material layers or that add layers to form electricaland electromechanical devices.

Spatial light modulators are an example of MEMS systems. Spatial lightmodulators used for imaging applications come in many different forms.Transmissive liquid crystal device (LCD) modulators modulate light bycontrolling the twist and/or alignment of crystalline materials to blockor pass light. Reflective spatial light modulators exploit variousphysical effects to control the amount of light reflected to the imagingsurface. Examples of such reflective modulators include reflective LCDs,and digital micromirror devices (DMD™).

Another example of a spatial light modulator is an interferometricmodulator that modulates light by interference. An interferometricmodulator may comprise a pair of conductive plates, one or both of whichmay be transparent and/or reflective in whole or part and capable ofrelative motion upon application of an appropriate electrical signal.One plate may comprise a stationary layer deposited on a substrate, theother plate may comprise a metallic membrane separated from thestationary layer by an air gap. Such devices have a wide range ofapplications, and it would be beneficial in the art to utilize and/ormodify the characteristics of these types of devices so that theirfeatures can be exploited in improving existing products and creatingnew products that have not yet been developed. An iMoD™ is one exampleof an interferometric light modulator. The iMoD employs a cavity havingat least one movable or deflectable wall. As the wall, typicallycomprised at least partly of metal, moves towards a front surface of thecavity, interference occurs that affects the color of light viewed atthe front surface. The front surface is typically the surface where theimage seen by the viewer appears, as the iMoD is a direct-view device.

SUMMARY

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

In various embodiments of the invention, a display device comprises anillumination apparatus configured to emit light of different color atdifferent times and at least one interferometric light modulating deviceilluminated by the illumination apparatus. In certain preferredembodiments, interferometric light modulating devices are illuminatedfor short durations with different color light, the durations of thetime being sufficiently short to produce color fusion or blending ofcolors as perceived by the human eye. The interferometric lightmodulating device may comprise a white interferometric light modulatingdevice that reflects white light in one state. The interferometric lightmodulating device may also have a reflectivity spectrum that includes aleast two color peaks.

In another embodiment, a display device is provided, comprising: atleast one interferometric light modulator configured to reflect light,said at least one interferometric light modulator configured to reflectlight comprising a spectral response including two or more reflectancepeaks in the visible spectrum; and a light source having an emissionspectra that includes at least one emission peak at least partiallyoverlapping one of said two or more reflectance peaks.

In another embodiment, a display device is provided, comprising: meansfor modulating light, wherein the means for modulating light is capableof reflecting light having a plurality of intensity peaks in the visiblespectrum; and means for selectively illuminating said means formodulating light with light including at least said plurality ofintensity peaks in the visible spectrum.

In another embodiment, a method of manufacturing an interferometriclight modulating device is provided, comprising: providing a pluralityof pixel elements, each pixel element comprising at least oneinterferometric light modulator configured to reflect light comprising aspectral response that includes two or more reflectance peaks in thevisible spectrum; and providing a light source configured to selectivelyilluminate said plurality of pixel elements with light having one ormore spectral peaks substantially overlapping said two or morereflectance peaks.

In another embodiment, an interferometric light modulating device,comprising: a plurality of pixel elements, each pixel element comprisinga plurality of interferometric light modulators switchable betweendifferent reflective states; an illumination apparatus configured toselectively illuminate the plurality of pixel elements with light ofdifferent color at different times; and a control system configured tocontrol the color of said light with which said pixel elements areilluminated.

In another embodiment, a display device is provided, comprising: anillumination apparatus configured to emit light comprising an emissionspectra having a variable spectral output; at least one light modulatingdevice configured to reflect light from said illumination apparatus,said at least one light modulating device comprising an optical cavityformed by a pair of reflective plates; and a control system configuredto control the spectral output of the illumination apparatus.

In another embodiment, an interferometric light modulating device isprovided, comprising: means for interferometrically modulating lightswitchable between different reflective states; and means forselectively illuminating said means for interferometrically modulatinglight with light of different color at different times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a released position and amovable reflective layer of a second interferometric modulator is in anactuated position.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIG. 6A is a cross section of the device of FIG. 1.

FIG. 6B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 6C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7A illustrates an interferometric modulator array of substantiallyidentical modulators.

FIG. 7B illustrates the integration of the modulator array illustratedin FIG. 7A with a waveguide and multi-colored light source.

FIG. 8 is a plot on axis of reflectivity versus wavelength of areflective response an exemplary interferometric modulator.

FIG. 9 provides a block diagram illustrating the spatial and temporalmixing that occurs in a system.

FIG. 10 provides a flowchart that illustrates the control of aninterferometric modulator array in conjunction with a multicolored lightsource.

FIG. 11 is an exemplary interferometric light modulator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In various embodiments of the invention, a plurality of interferometricmodulators are illuminated with an illumination apparatus that emitsdifferent color light at different times. This illumination apparatusmay emit different colors (e.g., red, green, and blue) in a sequencethat is repeated. This illumination apparatus may comprise, for example,a red, a green, and a blue light emitting diode. The interferometricmodulators may, in such a case, be illuminated with red light over afirst time period, with green light over a second time period, and withblue light over a third period. This colored light is reflected from theinterferometric modulators to a viewer. In certain preferredembodiments, the durations of the time periods are sufficiently short toproduce color fusion or blending of colors as perceived by the eye ofthe viewer. The interferometric light modulators may switch faster thanthe time period. The interferometric light modulating device maycomprise a white interferometric light modulating device that reflectswhite light in one state. This white light interferometric modulatorwill also reflect the color light from the illumination apparatus. Theinterferometric light modulating device may also have a reflectivityspectrum that includes at least two color peaks. These two color peaksmay overlap with colors emitted by the illumination apparatus.

Advantageously, various exemplary embodiments may comprise a pluralityof interferometric light modulators wherein each of the light modulatingelements includes an optical cavity that is designed to provideessentially the same optical response. In certain embodiments, forexample, when an optical cavity is closed on one of the interferometriclight modulators, the color black will be the spectral response.Conversely, when the optical cavity is open, light is reflected having apredetermined spectral response. This predetermined optical response maybe broadband white, such that a wide range of colors incident on themirror will be reflected with approximately equal intensity.Alternatively, this optical response may include a plurality of separatecolors peaks, such as red, blue and green color peaks, similar to thecolors produced by the illumination apparatus.

As described above, the illumination apparatus may comprise amulti-colored light source. The color(s) reflected by theinterferometric light modulators may be controlled by the spectrum oflight emitted by the multi-colored light source and directed towards thelight modulators. A control system may be provided that controls theinterferometric modulators so as to create images having the desiredcolors. In some embodiments, the control system may also control theoutput of the light source and thus the illumination of theinterferometric modulators. The control system may be referred to hereinas a control processor and may comprise one or more electronics devicesor other control or computational devices. The control system maycomprise, for example, a processor and an array controller. The controlsystem may comprise a microprocessor in some embodiments.

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theinvention may be implemented in any device that is configured to displayan image, whether in motion (e.g., video) or stationary (e.g., stillimage), and whether textual or pictorial. More particularly, it iscontemplated that the invention may be implemented in or associated witha variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as thereleased state, the movable layer is positioned at a relatively largedistance from a fixed partially reflective layer. In the secondposition, the movable layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable and highly reflective layer 14a isillustrated in a released position at a predetermined distance from afixed partially reflective layer 16 a. In the interferometric modulator12 b on the right, the movable highly reflective layer 14b isillustrated in an actuated position adjacent to the fixed partiallyreflective layer 16 b.

The fixed layers 16 a, 16 b are electrically conductive, partiallytransparent and partially reflective, and may be fabricated, forexample, by depositing one or more layers each of chromium andindium-tin-oxide onto a transparent substrate 20. The layers arepatterned into parallel strips, and may form row electrodes in a displaydevice as described further below. The movable layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes 16 a, 16 b) deposited on top ofposts 18 and an intervening sacrificial material deposited between theposts 18. When the sacrificial material is etched away, the deformablemetal layers are separated from the fixed metal layers by a defined airgap 19. A highly conductive and reflective material such as aluminum maybe used for the deformable layers, and these strips may form columnelectrodes in a display device.

With no applied voltage, the cavity 19 remains between the layers 14 a,16 a and the deformable layer is in a mechanically relaxed state asillustrated by the pixel 12 a in FIG. 1. However, when a potentialdifference is applied to a selected row and column, the capacitor formedat the intersection of the row and column electrodes at thecorresponding pixel becomes charged, and electrostatic forces pull theelectrodes together. If the voltage is high enough, the movable layer isdeformed and is forced against the fixed layer (a dielectric materialwhich is not illustrated in this Figure may be deposited on the fixedlayer to prevent shorting and control the separation distance) asillustrated by the pixel 12 b on the right in FIG. 1. The behavior isthe same regardless of the polarity of the applied potential difference.In this way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application. FIG. 2is a system block diagram illustrating one embodiment of an electronicdevice that may incorporate aspects of the invention. In the exemplaryembodiment, the electronic device includes a processor 21 which may beany general purpose single- or multi-chip microprocessor such as an ARM,Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051,a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessorsuch as a digital signal processor, microcontroller, or a programmablegate array. As is conventional in the art, the processor 21 may beconfigured to execute one or more software modules. In addition toexecuting an operating system, the processor may be configured toexecute one or more software applications, including a web browser, atelephone application, an email program, or any other softwareapplication.

In one embodiment, the processor 21 is also configured to communicatewith an array controller 22. In one embodiment, the array controller 22includes a row driver circuit 24 and a column driver circuit 26 thatprovide signals to a pixel array 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the released state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not releasecompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the released or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be released areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or releasedpre-existing state. Since each pixel of the interferometric modulator,whether in the actuated or released state, is essentially a capacitorformed by the fixed and moving reflective layers, this stable state canbe held at a voltage within the hysteresis window with almost no powerdissipation. Essentially no current flows into the pixel if the appliedpotential is fixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −Vbias, andthe appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Releasing the pixel is accomplished by setting theappropriate column to +Vbias, and the appropriate row to the same +ΔV,producing a zero volt potential difference across the pixel. In thoserows where the row voltage is held at zero volts, the pixels are stablein whatever state they were originally in, regardless of whether thecolumn is at +Vbias, or −Vbias. As is also illustrated in FIG. 4, itwill be appreciated that voltages of opposite polarity than thosedescribed above can be used, e.g., actuating a pixel can involve settingthe appropriate column to +V_(bias), and the appropriate row to −ΔV. Inthis embodiment, releasing the pixel is accomplished by setting theappropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or released states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and releases the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and release pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thepresent invention.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 6A-6C illustrate three different embodiments of themoving mirror structure. FIG. 6A is a cross section of the embodiment ofFIG. 1, where a strip of metal material 14 is deposited on orthogonallyextending supports 18. In FIG. 6B, the moveable reflective material 14is attached to supports at the corners only, on tethers 32. In FIG. 6C,the moveable reflective material 14 is suspended from a deformable layer34. This embodiment has benefits because the structural design andmaterials used for the reflective material 14 can be optimized withrespect to the optical properties, and the structural design andmaterials used for the deformable layer 34 can be optimized with respectto desired mechanical properties. The production of various types ofinterferometric devices is described in a variety of publisheddocuments, including, for example, U.S. published Application2004/0051929. A wide variety of well known techniques may be used toproduce the above described structures involving a series of materialdeposition, patterning, and etching steps.

As described above, in certain embodiments, the interferometricmodulators may be illuminated with light from an illumination apparatusthat varies the color of illumination provided at different times. Asequence of colors such as for example, red, green, and blue maytherefore be used to illuminate the interferometric modulators. Theinterferometric modulators selectively reflect this light to produce acolor image.

As described above, interferometric modulators can be provided in arraysand are addressed to provide the desired display. Addressing directs theselected modulator to provide a predetermined optical response. Theelements can be individually addressed or in the preferred embodimentcan be addressed by means of strobing one set of electrodes andproviding data on the other electrodes. (One preferred method ofaddressing reduces the number of control signals necessary to drive thedisplay. This is described in detail in U.S. Pat. No. 5,986,796,entitled “Visible Spectrum Modulator Arrays” assigned to the assignee ofthe present invention.)

Accordingly, various embodiments comprise a display having an array ofinterferometric modulators, which when combined with an appropriatelydriven multi-colored light source can be used to produce colored images.Such a display is capable of being used as either a direct view colordisplay or a projection color display. As described above, in certainembodiments a black state is produced when the interferometric modulatoris actuated with the optical resonance cavity collapsed. In the releasedposition with the cavity open, the interferometric modulators aredesigned to provide a predetermined reflection characteristic, which caneither be broadband white such that a range of colors incident on themirror will be reflected with approximately equal intensity or are tunedto have are reflectivity spectrum with a plurality of reflectance peaksoverlapping or corresponding to the colors transmitted by themulti-colored light source. When an array of modulators of the typedescribed above is combined with sequential illumination of the array bya set of primary colors such as red, green, and blue light, full colordirect-view and projection displays can be realized. Utilizinghigh-speed light sources, such as LEDs, it is possible to make thecolor-field time much shorter than the response time of the eye,allowing for color fusion.

By implementing a full color display to be realized using a uniformarray of interferometric modulators, the fabrication process of thedisplay array can be simplified because the interferometric modulatorshave as single air-gap height and uniform mechanical layer design. This,in turn results in inherent voltage matching, such that the opticalresponse to voltages applied to the electrodes will be substantiallyidentical. In addition, there will be a substantially identical fillfactor for each color because the total area of the pixel will be usedfor each color and the bit depth is independent of pixel layout. In oneembodiment, a display fabricated provides a wide color gamut by means ofproper light source selection, and allows for low power consumption inemissive-like mode in low ambient light level environments.

One exemplary embodiment provides three integrated parts: (1) aninterferometric modulator array designed to reflect with three or morereflectance peaks in the visible spectrum; (2) a light source capable ofemitting a set of primary colors, such as a light emitting diode or setof diodes capable of emitting a set of red, green and blue light withemission spectra chosen to match the reflectance peaks of theinterferometric modulator array; and (3) a light guide designed toilluminate the interferometric modulator array with the light from themulti-colored light source. The interferometric modulator array issequentially illuminated by red, green, and blue light. The light isguided on the array by one or more light guides. These light guides mayhave features (reflective or scatter features, etc.) such ascorrugations, causing a portion of the light to deflect and illuminatethe array at normal incidence. The light is modulated and at least aportion is reflected normally through the light guide to the viewer.

Another embodiment also provides three integrated parts: (1) aninterferometric modulator array designed to reflect with three or morereflectance peaks in the visible spectrum; (2) a light source capable ofa broadband spectrum of light including at least a partial overlap ofemission spectra corresponding to the reflectance peaks of theinterferometric modulator array; and (3) a spectral filter designed toilluminate the interferometric modulator array (or portions thereof)with a particular spectrum of light from the broadband light source.This embodiment may also provide a light guide designed to illuminatethe interferometric modulator array (or portions thereof) with the lightpassing through the spectral filter.

One embodiment of an exemplary array of interferometric modulators isillustrated in FIG. 7A. In particular, FIG. 7A shows two adjacentinterferometric modulators structures. Additional details regarding suchinterferometric modulators are described in above. For theinterferometric modulators shown in FIG. 7A, a thin film of absorbinglayer 205 is deposited on the substrate 202. In this exemplaryembodiment, the conducting/absorbing layer 205 is made from chrome andITO and substrate 202 may be made of glass. Above conducting/absorbinglayer 205, a dielectric layer 204, typically an oxide, is deposited.Support posts 206 are provided to suspend a mechanical/mirror element208 at a predetermined height above dielectric layer 204 designed toprovide an optical response. Additional geometries and materials used inthe fabrication of the interferometric modulator structure are discussedin detail in U.S. Pat. No. 5,835,255 and the aforementioned U.S. patentapplication Ser. No. 09/966,843. As described above, other variationsare possible.

In FIG. 7A, the two independent modulators have optical cavities 210 aand 210 b that determine the optical response of the modulators. Thesecavities can be actuated or released independently of one another. Inone embodiment, the modulators of the display all have essentially thesame optical response. However, the color they display will bedetermined by the color of the illuminating light source and they aredesigned to reflect multiple wavelengths of light. It will be understoodby one skilled in the art that the illustration of only two modulatorsis for illustrative purposes and that a display will have many moremodulators.

In the exemplary embodiment illustrated in FIG. 7A, the interferometricmodulators each employ the same air gap distance (d_(air)). As theoptical response is tuned as a function of the modes of the wavelengthof the reflected light, the cavity can be designed to reflect multiplewavelengths. Turning to FIG. 8, the cavity height (d_(air)) is selectedto be highly reflective in the released state for at least threewavelengths (λ1, λ2 and λ3) represented as peaks in reflectivity. In oneembodiment, these peaks correspond to the wavelength of the blue, greenand red light emitted by the multi-colored light source. It will beunderstood by one skilled in the art that the teachings disclosed hereinare equally applicable to the case when there are more or lessreflective peaks than are illustrated and to the case where themodulator provides a broadband response reflecting peaks across thevisible spectrum of light. For example, in one embodiment the cavityheight (d_(air)) is selected to be highly reflective in the releasedstate for at least two wavelengths, such as cyan and yellow. If peaks inreflectivity are present around wavelengths not corresponding to one ofthe colors of light transmitted by the light source, those peaks aresimply not employed and will not have a pronounced effect on theoperation. In another embodiment, the light modulator is a broadbandwhite light modulator providing a broadband response reflecting a widerange of wavelengths across the visible spectrum of light. The lightsource and/or the spectral filter will control what color is reflectedby the light modulator since it will reflect the light spectrum fed toit.

FIG. 7B illustrates an exemplary display configuration. Light source 256provides different color at different times. In the exemplaryembodiment, the light source is a light emitting diode, capable ofsequentially emitting primary colors of light. In the exemplaryembodiment, light source 256 will emit red light during a first timeinterval, green light during a second time interval and blue lightduring a third time interval. It will be understood by one skilled inthe art that the any light source capable of sequentially emittingcolors such as lamp & color wheels, rotating lamp & filter assemblies,and lamp/filter/rotating prism combinations may be used and need not belimited to the most common set of primary colors red, green and blue.

The light passes through one or more light guides 250. The light isdirected through light guide 250 onto interferometric modulator array252. Interferometric modulator array 252 is provided on substrate 254.Exemplary light guides may have features (reflective features, scatterfeatures, etc.) such as corrugations on the light guide that cause someof the light to deflect and illuminate the array at normal incidence.Although normal deflection of light towards the array 252 is ideal, anormal reflective angle may not be a dominate reflective angle, asillustrated by FIG. 7B. In turn, some of the light is modulated andreflected normally through the light guide to the viewer byinterferometric modulator array 252. Again, some of the light reflectedby the array 252 may be at a non-normal angle.

FIG. 9 provides a block diagram of an exemplary display. Controlprocessor 408 provides signals to display 400. Display 400 comprises alarge number of pixel elements. Pixel elements 402 a-402 i are providedfor illustrative purposes. Pixel elements 402 a-402 i are independentlyaddressable. Traditionally, pixel elements 402 a-420 i would comprisecolor specific sub pixels that would be responsible for displaying thecolors red, blue, or green. However in one embodiment, pixel elements402 a-402 i are capable of displaying all three colors and the colordisplayed is determined by the color of the light emitted by lightsource 410. In this particular embodiment, the pixel elements 402 a-402i are implemented using interferometric modulators.

The human eye in combination with the human brain integrates imageswhich are altered faster than the capacity to be viewed individually. Itis this integration that allows a sequence of images flashed at a rapidrate to appear to the viewer as continuous motion video. Thisintegrating aspect of human sight is exploited as described herein in adifferent manner. If the color red and the color blue are alternatelyflashed at a viewer at a rapid enough rate, the viewer will see thecolor purple because the brain will in essence integrate or low passfilter the rapidly changing images.

Accordingly, control processor 408 receives an indication of the desiredcolor to be displayed by each of the pixel elements 402 a-i. Controlprocessor 408 determines the ratio of red green and blue needed toproduce this color. Based on this ratio a first number ofinterferometric modulators 402 a-i will be selected to be in thereleased position (the cavity will be open) while light source 410 isemitting red light, a second number of interferometric modulators 402a-i will be selected to be in the released position (the cavity will beopen) while light source 410 is emitting green light, and a third numberof interferometric modulators 402 a-i will be selected to be in thereleased position (the cavity will be open) while light source 410 isemitting blue light. By strobing sequentially through the red, green andblue colors fast enough an arbitrarily large color gamut can berealized.

In order to adjust the intensity of the displayed color, controlprocessor 408 uses temporal dithering whereby the displayed color isflashed at a select number of the pixel elements 402 a-i atpredetermined intervals while the modulators of the select pixelelements 402 a-i are actuated. When a modulator of a pixel element 402a-i is actuated, the pixel element displays black. By integrating thisblack state into the flashed sequence, the intensity of the colorproduced as described above can be reduced. In the preferred embodiment,the two methods described above can be used in conjunction with oneanother to provide the optimal pixel pattern displaying both the correctintensity and color. That is to say, the frames actively displayingcolor can be combined with the frames displaying black to adjust theintensity.

In addition, various embodiments provide display flexibility bypermitting control processor 408 to control the color sequence, dutycycle and/or intensity of the light source 410. The output of the lightsource may be varied depending on the content of the images or otherconditions. For example, under conditions requiring fewer colors (smallcolor gamut), one or more light sources could be disabled. This has theadvantage of reducing power consumption of the display.

FIG. 10 illustrates the operation of control processor 408. At block500, control processor 408 receives color and intensity informationregarding pixel elements 402 a-i. In block 502, control processor 408determines the number and location of pixels set to reflect light fromlight source 410 during its red cycle, its blue cycle and its greencycle. In block 504, control processor 408 determines the duty cycle ofshading frames. The shading frames are black frames with all or aportion of the pixel elements 402 a-i actuated in order to reduce theintensity of the color displayed by integrating a predetermined amountof black shading into the displayed color. In block 506, controlprocessor 408 determines the color duty cycles, the rate of color changeand intensity of the light transmitted by light source 410. In block508, control processor 408 drives display 400 in accordance with theparameters determined above.

FIG. 11 provides an alternative structure for the interferometricmodulator. Modulator 600 comprises a lower electrode 622, typicallyfabricated from ITO. On top of electrode 622 is a first dielectric 620such as SiO₂ is deposited. Above dielectric 620 is deposited a thinlayer of absorber/conductor material 618 such as chrome and above theabsorbing layer is an electrically isolating layer 616, which isfabricated from a material such as Al₂O₃. A first set of posts 612 areprovided to support mirror 610 so as to form first optical cavity 614.The mirror 610 is typically fabricated from aluminum and may also act asan electrode. Above mirror 610 are a second set of posts 606, which areprovided to support dielectric layer 604, which in the exemplaryembodiment is composed of SiO₂. This results in the formation of secondcavity 608. Above dielectric layer 604 is a high electrode 602. Thismodulator when viewed from below will display black in the unactuatedstate. When a field is applied between mirror 610 and electrode 602,causing cavity 608 to collapse, the modulator will have a spectralresponse defined in part by a vertical dimension of the optical cavity.When a field is applied between mirror 610 and electrode 622, causingcavity 614 to collapse, the modulator becomes a broadband mirror capableof high reflectance of all frequencies of incident light. In someembodiments, layer 616 is very thin, thereby minimizing a separationdistance between the mirror 610 and a substrate (not depicted)configured below electrode 622 when the cavity 614 is collapsed. In oneembodiment, layer 616 is 100 Angstroms thick.

This modulator operates as described with respect to other exemplaryembodiments described above, but operates in a mode wherein theunactuated color is black, i.e. low reflectivity. This could have theadvantage of reducing the number of pixels that need to be actuated inorder to write an image, for example, in an image having a substantialportion that is black.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A display device, comprising: at least one interferometric lightmodulator configured to reflect light, said at least one interferometriclight modulator having a spectral response including two or morereflectance peaks in the visible spectrum; and a light source having anemission spectra that includes at least one emission peak at leastpartially overlapping one of said two or more reflectance peaks.
 2. Thedevice of claim 1, further comprising a light guide configured topropagate light to said at least one interferometric light modulator. 3.The display device of claim 2, wherein said light source includes aplurality of emission peaks at least partially overlapping a pluralityof said two or more reflectance peaks.
 4. The display device of claim 3,wherein the light guide is configured to select at least one of saidemission peaks.
 5. The display device of claim 1, wherein said at leastone interferometric light modulator comprises an optical cavity formedby a pair of reflective surfaces having a gap therebetween.
 6. Thedisplay device of claim 5, wherein said gap defines a cavity height thatproduces said two or more reflectance peaks in said spectral response.7. The display device of claim 1, further comprising a plurality ofinterferometric light modulators, wherein each of the plurality ofinterferometric light modulators has an optical cavity comprising anopen state and a closed state, wherein the plurality of interferometriclight modulators are configured to have essentially the same spectralresponse in an open state and essentially the same spectral response ina closed state.
 8. The display device of claim 1, wherein said spectralresponse of said at least one interferometric light modulator includesthree or more reflectance peaks in the visible spectrum, said three ormore reflectance peaks comprising red, green and blue color peaks. 9.The display device of claim 1, further comprising an array of pixelelements, each pixel element comprising at least one interferometriclight modulator.
 10. The display device of claim 9, wherein said controlsystem is configured control reflectance of said at least oneinterferometric modulator in said pixel elements such that said pixelelements display said image.
 11. The display device of claim 9, furthercomprising a control system configured to receive a display signal foran image and configured to control illumination of said pixel elementssuch that said pixel elements display said image.
 12. The display deviceof claim 11, wherein said control system is configured to control acolor sequence, duty cycle, or intensity of light with which said pixelelements are illuminated.
 13. The display device of claim 1, wherein thelight source comprises a light emitting diode.
 14. A display device,comprising: means for interferometrically modulating light, wherein themeans for modulating light is capable of reflecting light having aplurality of intensity peaks in the visible spectrum; means forselectively illuminating said means for interferometrically modulatinglight with light including at least said plurality of intensity peaks inthe visible spectrum; and means for controlling the selectiveillumination of said means for interferometrically modulating light. 15.The display device of claim 14, wherein said means for controlling theselective illumination of said means for interferometrically modulatinglight is configured to control a color sequence, duty cycle, orintensity of light with which said means for interferometricallymodulating light is illuminated.
 16. The display device of claim 15,further comprising means for directing light from said means forilluminating to said means for modulating light.
 17. The display deviceof claim 14, wherein the plurality of intensity peaks in the visiblespectrum comprises either red, green, and blue color peaks or cyan andyellow color peaks.
 18. A method of manufacturing an interferometriclight modulating device, comprising: providing a plurality of pixelelements, each pixel element comprising at least one interferometriclight modulator having a spectral response that includes two or morereflectance peaks in the visible spectrum; and providing a light sourceconfigured to selectively illuminate said plurality of pixel elementswith light having one or more spectral peaks substantially overlappingsaid two or more reflectance peaks.
 19. The method of claim 18, furthercomprising positioning a spectral filter in an optical path between saidlight source and said pixel elements, said spectral filter configured toproduce said one or more spectral peaks.
 20. The method of claim 18,further comprising positioning a light guide with respect to said lightsource and said pixel elements to convey light from said light source tosaid pixel elements.
 21. The method of claim 20, wherein said lightguide is configured to produce said one or more spectral peaks.
 22. Themethod of claim 21, wherein the interferometric light modulators eachcomprise an optical cavity formed by a pair of reflective surfacesseparated by a distance.
 23. The method of 18, wherein the at least oneinterferometric light modulator of the plurality of pixel elements eachcomprising an optical cavity having an open state and a closed state,wherein the at least one interferometric light modulator of theplurality of pixel elements are configured to have essentially the samespectral response in an open state and essentially the same spectralresponse in a closed state.
 24. The method of claim 18, wherein said atleast one interferometric light modulator is configured to reflect lightincluding three or more intensity peaks in the visible spectrum, saidthree or more intensity peaks comprising red, green and blue colorpeaks.
 25. The method of claim 18, further comprising providing acontrol system configured to control selective illumination of the pixelelements with said one or more spectral peaks.
 26. The method of claim25, wherein said control system is configured to control color sequence,duty cycle, or intensity of light with which said pixel elements areilluminated.
 27. The method of claim 25, wherein said control system isconfigured to switch said interferometric modulators in said pixelelements between different output states.
 28. The method of claim 18,wherein the light source comprises a light emitting diode.
 29. Aninterferometric light modulating device, comprising: a plurality ofpixel elements, each pixel element comprising an interferometric lightmodulator switchable between different reflective states; and anillumination apparatus configured to selectively illuminate theplurality of pixel elements with light of different color at differenttimes.
 30. The device of claim 29, further comprising a control systemconfigured to control sequential illumination of said pixel elementswith said color light to produce a desired color by color fusion. 31.The device of claim 29, wherein further comprising a control systemconfigured to control said reflective states of said pixel elements. 32.A display device, comprising: an illumination apparatus configured toemit light comprising an emission spectra having a spectral output thatvaries with time; at least one light modulating device configured toreflect light from said illumination apparatus, said at least one lightmodulating device comprising an optical cavity formed by a pair ofreflective surfaces; and a control system configured to vary thespectral output of the illumination apparatus.
 33. The display device ofclaim 32, wherein said at least one light modulating device is abroadband light modulating device.
 34. The display device of claim 32,wherein said control system is configured to select different reflectivestates of the at least one light modulating device.
 35. Aninterferometric light modulating device, comprising: means forinterferometrically modulating light switchable between differentreflective states; and means for selectively illuminating said means forinterferometrically modulating light with light of different color atdifferent times.